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SBI3U Content Test Review > Meiosis > Flashcards

Meiosis Flashcards

1
Q

What happens during asexual reproduction?

A

Offspring have the same chromosomes as parents and are genetically-identical

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2
Q

What happens during sexual reproduction?

A

There are differences between parent and offspring chromosomes which creates genetic diversity.

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3
Q

What is fertilization? What does it do?

A

The union of gametes; It doubles chromosome number – so to prevent chromosome number from doubling each generation, sex cells must be haploid.

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4
Q

What does meiosis enable?

A

The sexual life cycle of eukaryotes by producing such haploid cells.

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5
Q

What is meiosis?

A

A reduction division of the nucleus to form haploid gametes.

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6
Q

What does the process of meiosis do? (It divides)

A

It divides one diploid eukaryotic nucleus to form four haploid nuclei

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7
Q

How many times is the original diploid cell divided in this process?

A

It divided twice in this process – Meiosis I and Meiosis II

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8
Q

Since the chromosome number is halves, what is meiosis called?

A

A reduction division

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9
Q

What are somatic cells? Are they haploid or diploid?

A
  • ‘Body’ Cells
  • Diploid (2n)
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10
Q

What are sex cells? Are they haploid or diploid?

A

-Gametes (egg/sperm)
-Haploid (n)

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11
Q

What are gametes?

A

-Males: Sperm are produced in the male gonads called the testes.
- Females: Ova (Ovum = si.) are produced in the female gonads called the ovaries.

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12
Q

What happens during fertilization? What is the result called?

A
  • During ovulation, an ovum is released from the ovary and transported to an area where fertilization can occur.
    -The result is called a zygote
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13
Q

What is the process of fertilization?

A

Sperm + Ovum (egg) (arrow-fertilization) Zygote

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14
Q

What are homologous chromosomes?

A

Chromosomes of the same size and structure, with the same sequence of genes (i.e. same genes at the same gene loci)

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15
Q

Although homologous chromosomes have the same genes, what might they have that is different?

A

Different alleles for the gene.

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16
Q

In humans, how do homologous chromosomes exist?

A

In humans, one of each chromosome type comes from the mother and one of each type comes from the father to make 22-23 homologous pairs

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17
Q

What is technically not homologous?

A

Since males have one X and one Y chromosome as their 23rd pair, it is technically not homologous.

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18
Q

What do homologous chromosomes have? (in terms of alleles)

A

Alleles for the same genes at specific loci

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19
Q

What do sister chromatids of duplicated chromosomes have?

A

Same alleles for each gene.

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20
Q

What do homologous chromosomes have?

A

The same structure?

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21
Q

Are somatic cell nuclei (body cells) haploid or diploid

A

Diploid (2n)

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22
Q

What do somatic cell nuclei contain?

A

A homologous pair of each chromosome-one of the pair is paternal, inherited from the father, and the other is maternal, inherited from the mother.

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23
Q

Homologous chromosomes have the same what? (everything)

A

Same size and structure, and carry the same genes at the same loci.

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24
Q

What varies in homologous chromosomes?

A

The alleles carried at each locus

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25
Q

22 of the human chromosome pairs are what? The other pair, the sex chromosomes, are what?

A

Homologous; Non-homologous

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26
Q

In humans, what set number of chromosomes determine gender?

A

The 23rd set

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27
Q

Describe the X Chromosome

A

Large with a centromere in the middle (2000+ genes)

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28
Q

Describe the Y Chromosome

A

Small with a centromere near the top (less than 100 genes)

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29
Q

What does the X chromosome carry?

A

Genes necessary to human development

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30
Q

What does the Y chromosome carry?

A

Genes needed for male development

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31
Q

What are the other 44 chromosomes in the human body called? What do they carry? What are their set numbers?

A
  • Autosomes
  • They carry only non-sex-related genes
  • Homologous pairs 1-22
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32
Q

Show the process of Spermatogenesis

A
  • Primary Spermatocyte (2n = 46) (arrow)
  • Meiosis I:
  • Secondary Spermatocyte (n = 23)
  • Secondary Spermatocyte (n=23);
    -Meiosis II:
    -Sperm (n) (n = 23)
    -Sperm (n) (n=23)
    -Sperm (n) (n=23)
    -Sperm (n) (n=23)
33
Q

Summarize the process of Spermatogenesis in one point

A

4 sperm cells are produced from each primary spermatocyte

34
Q

Show the process of Oogensis

A

-Primary Oocyte: Secondary Oocyte and Polar Body
-Secondary Oocyte: Egg and Polar Bodies
-Polar Body: More Polar Bodies

35
Q

Summarize the process of oogenesis in one point

A

The polar bodies die…only one ovum (egg) is produced from each primary oocyte

36
Q

What occurs during Interphase? (4 points)

A
  • In the S-phase of the interphase before meiosis begins, DNA replication takes place.
  • Chromosomes are replicated and these copies are attached to each other at the centromere.
  • The attached chromosome and its copy are known as sister chromatids.
  • Following S-phase, further growth and preparation take place for meiosis.
37
Q

What is the main event of Interphase?

A

-A homologous pair of chromosomes replicates during S-phase of interphase

38
Q

What occurs during Prophase I? (4 points)

A

-Nuclear membrane dissolves
-Centrioles migrate to the poles of the cell
-Crossing-over between non-sister chromatids can take place. This results in recombination of alleles and is a a source of genetic variation in gametes.
-The homologous chromosomes associate with each other to form bivalents (synapsis).

39
Q

During prophase I, what happens to the homologous pair?

A

It associates during prophase I through synapsis, making a bivalent.

40
Q

In prophase I, what takes place?(2 points)

A
  • Crossing-over might take place between non-sister chromatids, leading to recombination of alleles.
    -The point of crossing-over between non-sister chromatid is called the chiasma (pl. chiasmata)
41
Q

What does crossing-over do?

A

Increases genetic variation through recombination of linked alleles.

42
Q

What are the three main stages of crossing-over?

A

-Synapsis: Homologous chromsomes associate
-Chiasma Formation: Neighbouring non-sister chromatids are cut at the same point.
-Recombination: As a result, alleles are swapped between non-sister chromatids.

43
Q

What does crossing-over lead to?

A

Crossing over leads to more variation in gametes.

44
Q

What occurs during Metaphase I? (3 points)

A
  • Random orientation occurs - each bivalent aligns independently and hence the daughter nuclei get a different mix of chromosomes.
  • This is a significant source of genetic variation: there are 2n possible orientations in metaphase I and II.
  • That is 223 in humans – or 8,388,068 different combinations in gametes!
45
Q

How does variation occur in Metaphase I?

A

-Through Mendel’s Law of Independent Assortment

46
Q

What does Mendel’s Law of Independent Assortment state?

A

The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.

47
Q

What is the difference between Random Orientation and Independent Assortment in Metaphase I?

A
  • Random Orientation refers to the behaviour of homologous pairs of chromosomes (metaphase I) or pairs of sister chromatids (metaphase II) in meiosis.
  • Independent assortment refers to the behaviour of alleles of unlinked genes as a result of gamete production (meiosis).
48
Q

What stages of Meiosis does genetic variation occur?

A

-Prophase I
-Metaphase I
-Metaphase II

49
Q

What genetic variation occurs in Prophase I?

A
  • Crossing-over between non-sister chromatids results in recombination of alleles
50
Q

What genetic variation occurs in Metaphase I and Metaphase II?

A

Random orientation of the homologous chromosomes means there are 2n possible orientations in metaphase I and II. That is 223 in humans – or 8,388,068 different combinations in gametes!

51
Q

What occurs during Metaphase I? (3 points)

A
  • Allele have a 50 percent chance of moving to a particular pole.
  • The direction in which one bivalent aligns does not affect the alignment of other bivalents.
  • Therefore different allele combinations should always be equally possible (if the gene loci are on different chromosomes – this does not hold for linked genes)
52
Q

What occurs during Anaphase I? (3 points)

A
  • Spindle Fibres contract
  • Homologous pairs are separated and pulled to opposite poles
  • This is reduction division
53
Q

In anaphase I, what is separated but what remains attached? What is this called?

A

The homologous pair is separated; the sister chromatids remain attached; this is the reduction division

54
Q

What occurs during Telophase I? (4 points)

A
  • New nuclei form and the cytoplasm begins to divide by cytokinesis
  • The nuclei are no longer diploid
  • They each contain one pair of sister chromatids for each of the species’ chromosomes
  • If crossing over and recombination has occurred then the sister chromatids will not be exact copies
55
Q

What occurs during Prophase II?

A
  • The nuclei break down
  • No crossing over
56
Q

What occurs during Metaphase II? (4 points)

A
  • Pairs of sister chromatids align at the equator.
  • Spindle fibres form and attach at the centromeres
  • Random orientation again contributes to variation in the gametes, though not to such an extent as in metaphase I
  • This is because there is only a difference between chromatids where crossing over has taken place
57
Q

What happens during Anaphase II? (3 points)

A
  • Spindle fibres contract and the centromeres are broke
  • The pairs of sister chromatids are pulled to opposing poles
  • Non-disjunction here will lead to two gametes containing the wrong chromosome number
58
Q

What occurs during Telophase II? (4 points)

A
  • New haploid nuclei are formed
  • Cytokinesis begins, splitting the cells
  • The end result of meiosis is four haploid gamete cells
  • Fertilization of these haploid gametes will produce a diploid zygote
59
Q

Meiosis is prone to what? What happens in some cases?

A
  • Meiosis is prone to error.
  • In some cases, chromosomes fail to split properly in either Anaphase I or Anaphase II.
60
Q

What is chromosomes failing to split properly in either Anaphase I or Anaphase II called?

A

Non-Disjunction

61
Q

What does Non-Disjunction result in?

A

The result is the production of a gamete with an extra chromosome (Trisomy) or a missing chromosome (Monosomy)

62
Q

What are incidences of Non-Disjunction strongly correlated with?

A

Maternal age

63
Q

What can happen during Non-Disjunction?

A
  • In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
  • Non-disjunction leads to changes in chromosome number.
64
Q

When can non-disjunction occur?

A

In anaphase I or anaphase II

65
Q

What does non-disjunction produce? (with regards to gametes)

A

Gametes with an abnormal number of chromosomes; fertilization adds the homologous chromosomes.

66
Q

What does non-disjunction result in? (zygotes and somatic cells)

A

A zygote and somatic cells with a trisomy of one chromosome, which can be fatal or cause disorders.

67
Q

What are some non-disjunction syndromes and what is the chromosome abnormality?

A

-Turner Syndrome: One X and no Y sex chromosome
-Klinefelter Syndrome: Two X and one Y sex chromosome
-Patau Syndrome: Trisomy of chromosome 13
-Edwards Syndrome: Trisomy of chromosome 18

68
Q

What are two methods of Non-Disjunction Detection?

A

-Amniocentesis
-Chorionic Villus Sampling

69
Q

Where are the cells sampled from during Amniocentesis?

A

-Fetal cells are obtained from fluid in the amniotic sac where the fetus is held during the pregnancy.

70
Q

How are cells obtained during Amniocentesis?

A

Ultrasound is used to guide a large needle through the abdomen into the amniotic sac?

71
Q

What is the risk of miscarriage in Amniocentesis?

A

1%

72
Q

Where are cells sampled from in Chorionic Villus Sampling?

A

Fetal cells obtained from the chorion-a part of the placenta.

73
Q

How are cells obtained in Chorionic Villus Sampling?

A

A sampling tool enters through the vagina - can be done earlier in the pregnancy

74
Q

What is the risk of miscarriage in Chorionic Villus Sampling?

A

2%

75
Q

What is karyotyping?

A

A pre-natal test used to check for gender, and non-disjunction disorders.

76
Q

How do you deduce sex from a karyotype?

A

XX = Female
XY = Male

77
Q

How do you deduce chromosomal abnormalities from karyotypes?

A
  • Errors in Meiosis can lead to the formation of zygotes with abnormal chromosome numbers (In humans, this is any number that is not 46 – 44 Autosomes, 2 Sex chromosomes)
  • Trisomy: Having a third (extra) chromosome
  • Monosomy: Having only one chromosome
78
Q

What does Down Syndrome result from?

A

Trisomy of the 21st chromosome

79
Q

Describe Down Syndrome

A
  • The most common genetic condition
  • Causes physical and mental development delays
  • 50-60 year life expectancy
  • ~6,000 babies each year in the U.S. (Risk is strongly correlated with maternal age)

SBI3U Content Test Review (9 decks)

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